1. Field of the Invention
The present invention relates to a method and an apparatus for avoiding a collision between each of radio frequency identification (RFID) readers, and for primarily granting an important RFID reader a frequency channel usage right.
2. Description of the Related Art
A radio frequency identification (RFID) reader receives a response, which is related to a command transmitted from the RFID reader itself, from an RFID tag, thereby recognizing the RFID tag. At this point, in the case where a plurality of RFID readers, which adjacently exist, use the same frequency or in the case where a plurality of RFID readers simultaneously transmit a command to one RFID tag, the RFID readers can mutually cause an interference, and this phenomenon is called an RFID reader collision or a reader collision between each of the RFID readers.
The RFID market has been rapidly developed such that RFID readers and RFID tags are used in various fields. Thus, in the case where the RFID market is further developed such that many RFID readers are used in a limited space, if an item, which has an attached RFID tag to be read by an RFID reader, is not recognized by the RFID reader due to an RFID reader collision, then a severe problem can occur.
In U.S. Patent Publication No. 2005/0088284 A1, dated 28 Apr. 2005, entitled “Method and system of using an RFID reader network to provide a large operation area” (hereinafter, referred to as ‘conventional invention’), a “Listen Before Talk” method is provided to avoid such RFID reader collision between each of the RFID readers. The “Listen Before Talk” method provides a method of synchronizing all of the RFID readers, so that the RFID readers simultaneously listen and talk. The “Listen Before Talk” method, according to the conventional invention, checks (Listen) whether a randomly selected frequency channel is used by an adjacent RFID reader, before an RFID reader reads an RFID tag. When a status of the randomly selected frequency channel is “Idle”, the RFID reader reads (Talk) the RFID tag. When the status of the randomly selected frequency channel is not “Idle”, the RFID reader randomly selects another frequency channel and repeats the aforementioned process. If all of frequency channels are in use, the RFID reader repeats the process in the next cycle.
The conventional invention synchronizes all RFID readers via an aerial wire interface such as an antenna. However, in the case where a mobile RFID reader or a handheld RFID reader, which does not have a synchronization function, is separately used, it is difficult to use them after synchronization. Also, in the case where RFID readers are used in a limited space, it is difficult to grant an important RFID reader priority of frequency channel usage.
Also, according to the conventional invention, a RFID reader wirelessly checks a channel used by an adjacent RFID reader, and thus, accuracy, in terms of the checking of whether the adjacent RFID reader uses a frequency channel, is degraded.
Therefore, it is necessary to divide the RFID readers according to types of the RFID readers, to set frequency channels to be used by the divided RFID readers, and to prevent RFID readers of other types from using the set frequency channels.